The Diels-Alder adducts of non-polymeric mono- and diolefins with halocyclopentadienes, particularly cyclopentadienes wherein the carbon atoms of the conjugated double bonds are completely substituted with halogen, i.e. perhalogenated, are known and have become commercially important as fire retardant additives for various polymers (see e.g., U.S. Pat. No. 3,403,036) and as insecticides (see U.S. Pat. No. 2,635,977, U.S. Pat. No. 3,356,688).
The preparation of such solid adducts has been carried out either by direct combination, i.e. by reaction in bulk, of the reactants at atmospheric pressure or superatmospheric pressure (see e.g. U.S. Pat. No. 3,050,567) or by heating an organic solvent solution of the reactants (see e.g. col. 3, lines 46-47 of the aforementioned U.S. Pat. No. 3,050,567).
In the first of these prior art procedures the adduct is usually obtained in low yield and in a crude form which requires tedious and costly purification procedures. Moreover the product is often solidified with difficulty and when recovered in solid form is in the form of a massive crystalline body or aggregate which is difficult to break up into finely divided particles using conventional techniques such as trituration or heating with an organic solvent.
In the second procedure the use of organic solvents is expensive due to the necessity of recovering them and they are hazardous to personnel and equipment. In many instances, the adducts also solidify from the solvent solution as relatively large crystals which require pulverization prior to use as fire retardant additives since it is generally known that to be most effective in this application and to have the least effect on the physical properties of the polymer composition, the particle size of the additive should be as small as possible.
It is known to carry out the Diels-Alder reaction of open chain dienes e.g. 1,3-butadiene and beta chloro-1,3-butadiene, with olefinic and diolefinic dienophiles in aqueous emulsion or suspension as disclosed in U.S. Pat. No. 2,217,632; 2,222,357 and 2,262,002 but none of these references suggest use of an emulsion reaction technique to provide a finely divided particulate product. Many such Diels-Alder reactions of open chain dienes are distinguished from the corresponding Diels-Alder reactions of halocyclopentadienes in producing a liquid rather than a solid adduct, i.e, an adduct which is a solid at ambient temperature. Moreover the Diels-Alder adduction of such open chain dienes is distinguished from the diels-Alder adduction of the halocyclopentadienes on the basis of the known extensive difference in the Diels-Alder reactivity between such open chain dienes and cylic dienes such as the halocyclopentadienes. The sensitivity of the Diels-Alder reaction to such steric factors is more particularly discussed in A. Wasserman, "Diels-Alder Reactions", Elsevier Publishing Company, 1965, see especially Chapter 5.
It is also known to carry out in aqueous suspension the Diels-Alder reaction of an oleginic dienophile, e.g. maleic anhydride, with furan, a heterocyclic diene, as disclosed in O. Diels et al. Ann. 490 243 (1931), see especially p. 247. The reference reaction undesirably provides an adduct in the form of large flakes (see p. 247, seventh line from the bottom of the page of O. Diels et al. op. cit.). Moreover, the adduction reaction of the O. Diels et al. reference is distinguished from those of halocyclopentadienes in employing a heterocyclic diene reactant i.e. furan, rather than a homocyclic diene reactant as in the Diels-Alder reactions of the halocyclopentadienes.
It is further known to carry out in aqueous emulsion the Diels-Alder reaction of non-polymeric mono- and diolefinic dienophiles with cyclopentadiene devoid of halogen substituents as is disclosed in aforementioned U.S. Pat. No. 2,262,002. However the Diels-Alder reactions of non-halogenated cyclopentadiene are distinguished from those of the halocyclopentadienes by the known large difference in Diels-Alder reactivity between non-halogenated dienes and the corresponding halogenated dienes as indicated, for example, by a comparison of the Diels-Alder reaction rates of butadiene and chloro butadiene and of cyclopentadiene and hexachlorocyclopentadiene with the same dienophile as disclosed in S. Patai, editor, "The Chemistry of Alkenes" Interscience Publishers 1964, p. 921, Table 22.
U.S. Pat. No. 3,444,154 discloses the condensation of halocyclopentadienes and polymerized diolefins in aqueous emulsion. The reference, which also does not disclose the use of the emulsion reaction technique to achieve small product particle sizes, relates to a reaction wherein the dienophile reactant and the product are invariably polymeric substances and hence, distinguished from the Diels-Alder reactions of halocyclopentadienes with nonpolymeric mono- and diolefinic dienophiles wherein the reactants and products ae non-polymeric substances and the dienophiles contain at most, two olefinic carbon to carbon double bonds per molecule. The reaction of the reference is further distinguished from the Diels-Alder reaction of halocyclopentadienes with non-polymeric mono- and diolefinic dienophiles in not proceeding to substantially complete adduction of the unsaturation in the polymeric reactant, i.e. even under the most drastic reaction conditions and/or in the presence of stoichiometric excesses of the diene no more than about 49-83% of the ethylenic unsaturation in the diolefin polymer is adducted. (See for example, Example 4 of U.S. Pat. No. 3,444,154 wherein use of about a two hundred mole percent excess of hexachlorocyclopentadiene produces only about 82.9% adduction).